The present invention relates to an electron beam lithographic method which forms electronic circuitry (a pattern) on a semiconductor wafer using an electron beam.
A conventional lithography by an electron beam consists, in general, of sectionalizing a pattern to be lithographed and lithographing the sectionalized patterns successively.
So far, however, attention has not been given to a sufficient degree to minimize the number of sections of the pattern. In particular, when a side of the pattern before sectionalizing for lithography consists of a quadratic curve or a like curve such as a circle or an arc, it is necessary to approximately express the curve by a set of rectangular beams to lithograph it. In this case, however, the energy distribution of the electron beam loses stability unless the sectionalizing is suppressed as much as possible, and the precision of lithography is deteriorated.
The problem in this regard will be described in further detail in conjunction with the drawings.
FIG. 3 shows a pattern to be lithographed, and the data relating to the pattern are given as input data. The input data in this stage are called basic data, and the pattern thereof is called a basic pattern. FIG. 4 shows a lithographic pattern sectionalized by a conventional lithographic method when a closed pattern (formed of three line segments 7a, 7b and 7c) having at least one side of a curve 7c (arc in FIG. 3) is lithographed while effecting the black-white reversal processing necessary for the electron beam processing. As will be understood from FIG. 4, a curve must be expressed in steps by a set of quadrilaterals. By such a lithographic method, however, a large rectangle 8b is formed near a point 6b on the left side of FIG. 4, where the inclination of the curve 7c is loose. But narrow rectangles 8a are formed in a large number as the inclination of the curve 7c becomes steep, for example, near a point 6a at which the inclination of the curve 7c is a greatest value. However, when such narrow rectangles 8a are lithographed, the dimensional precision of pattern is adversely affected with respect to the amount of irradiation (amount of accumulated energy) of the electron beam. Furthermore, in the lithographic pattern reversed in black-white, particularly, in the case where the curve 7c is separated away from a border line 9b, narrow rectangles 8a are formed in great numbers. The precision decreases with an increase in the distance of separation.
One such conventional lithographic method is disclosed in Japanese Patent Laid-Open No. 154729/1987.
Moreover, examples of sectionalizing of lithographic data are disclosed in U.S. Pat. No. 4,132,898 and Japanese Patent Laid-Open No. 251718/1989 which, however, do not imply any method of lithography with a precision high enough to overcome the aforementioned problem.